Recently, portable devices that are driven by secondary batteries and carry out short distance wireless communication using, for example, Radio Frequency IDentification (RFID), are in widespread use (see Japanese Laid-Open Patent Application No. 2009-65426). Concerning such a portable device, it is demanded to miniaturize an antenna provided inside. However, if the antenna is miniaturized, the communication performance may be degraded due to gain deterioration. Therefore, in a recent portable device, ingenuity is exercised to contain the antenna inside in a manner of conserving space while maintaining the communication performance.
For example, techniques of forming an antenna that has a film-like shape to be affixed to a battery pack including a secondary battery, forming an antenna to be long and thin to be placed at a side corner or a lower corner of a portable device, and so forth, are known.
However, in these techniques, the antennas may have shapes derived from free spaces left inside the portable devices. Therefore, the shapes and/or the places of the antennas may depend on the shapes and/or the sizes of the portable devices.
Therefore, it may be necessary to consider the shapes and/or the places of the antennas for the respective portable devices, one by one. Further, depending on the places of the antennas, the impedances between the antennas and subsequent circuits may be changed. Therefore, it may be necessary to adjust the impedances and so forth for the respective portable devices, one by one. Thus, the processes required for mounting the antennas may be complicated and/or troublesome.